The manufacture of glass bottles begins with the preparation of raw materials. Sand and soda ash are measured in precise quantities, mixed together and conveyed to storage silos located over large melting furnaces. The mixed materials are continuously metered into the furnaces to replace molten glass which is dispensed from the furnaces after melting.
The furnaces are heated by a combination of natural gas and electricity and are operated at a temperature of over 2500 degrees Fahrenheit. The melted mixture of raw materials forms molten glass which flows from the furnaces through refractory channels, also known as forehearths, to a position over bottle forming machines.
A bottle forming machine known in the industry as an "I.S. machine" draws the glass into individual gobs and drops each gob into a blank mold. The blank mold forms a bottle preform, also referred to as a parison. The preform is transferred to a blow mold where it is blown by compressed air into a bottle. Each blow mold cavity typically contains indicia provided on a bottom wall thereof which embosses each bottle with code characters indicating the mold cavity in which it was formed.
The molds are lubricated by oil-borne carbon. The hot mold vaporizes the oil and some of the carbon immediately upon contact, leaving most of the carbon deposited upon the mold. Thus, the area around the mold is an extremely dirty environment filled with oil and carbon vapors and condensate.
An I.S. machine typically has between six and sixteen individual sections, with each section having from one to four blow mold cavities. Each section may be capable of manufacturing one to four bottles at a time. A typical eight section, triple gob, I.S. machine used in the production of beer bottles may produce 270 beer bottles per minute.
After the bottles have been blown, they are transferred from the respective blow mold cavities onto a moving conveyor belt. The bottles are positioned on the moving conveyor belt in a single line in a sequence corresponding to the sequence of the blow mold cavities in which the bottles were formed. The finished bottles transferred onto the conveyor from the blow mold are still red hot (approximately 1,000 degrees Fahrenheit). These hot bottles are conveyed by the conveyor belt through a hot end coating hood where they are chemically treated with a stannous chloride compound for strengthening. Vapors from the hot end coating hood also contribute significantly to the harsh environment found at the "hot end" of the bottle production line.
After passing through the hot end coating hood, the hot bottles are conveyed through an annealing oven or lehr where they are reheated and then cooled in a controlled manner to eliminate stresses in the glass. This annealing process typically takes from 20 to 30 minutes. The annealing process is the last process which takes place at the hot end of the production line. The portion of the production line downstream from the annealing oven is referred to as the "cold end" of the production line. In contrast to the hot end, the cold end is neither hot nor dirty. At the cold end of the production line, bottles are conveyed through a series of inspection devices. Typical prior art inspection devices include a squeezer which physically squeezes each bottle to check its sidewall strength. Another prior art cold end inspection device is referred to in the industry as a total inspection machine or T.I.M. which is sold by Emhart Glass having a business address of 123 Day Hill Road, Windsor, Conn. 06095. The total inspection machine physically engages each bottle and checks the size of the bottle neck opening and the thickness of the bottle sidewall and reads the code on the bottle bottom wall to determine the mold of origin. On a statistical sampling basis, the T.I.M. also sends bottles off line to be tested for burst strength, weighing, and measuring. Reports generated from the T.I.M. correlate bottle defects with the mold of origin. Another typical prior art inspection device is known as a "super scanner" sold by Inex, 13327 U.S. 19 North, Clearwater, Fla. 34624. The super scanner operates on each bottle on line. It initially scans a bottle, then engages and rotates the bottle approximately 90 degrees and scans it again. The super scanner uses image analysis to perform certain dimensional parameter checks of the bottle.
At both the T.I.M. and the super scanner inspection stations, defective bottles may be rejected by a cold end rejection device. After passing through the cold end inspection stations, bottles are transferred to a case packer machine, placed into a cardboard carton and conveyed to a palletizer machine for being placed in pallets. Loaded pallets are then shipped to a filling facility, such as a brewery.
A problem experienced with traditional glass bottle manufacturing operations as described above results from the fact that the bottle inspection stations are located at the cold end of the bottle production line. If a particular blow mold cavity begins producing defective bottles, e.g. as a result of a foreign object in the mold, the first defective bottle produced will not be detected until 30 to 40 minutes after its formation in the blow mold. As a result of this detection delay, the defective mold cavity will have continued to produce hundreds of defective bottles during the period between the first defective production and discovery of the first defective bottle. Furthermore, unless the defect is a defect of the type discovered by the T.I.M. machine which also identifies each bottle with a blow mold, the mold causing the problem will not be immediately apparent to the operator. As a result, the production operation must be shut down and each of the mold cavities of the I.S. machine must be inspected to detect the origin of the problem. Such shut down and inspection may be very time consuming and results in significant production loss in addition to the scrap produced by the defective mold cavity. Locating an inspection machine at the hot end of the bottle production line is difficult for a number of reasons: (1) as a result of the elevated temperature of the bottles at the hot end of the line, any engagement of the bottles by an inspection machine as is conventional with cold end inspectors would result in deformation of the bottle surface producing an ascetically unacceptable bottle; (2) the heat of the bottles at the hot end causes the bottles to glow and would thus make reading of mold origin indicating characters on the base of the bottle extremely difficult or impossible; (3) the contaminants in the atmosphere at the hot end of the line tend to coat the surface of any optical device used to image the bottles rendering imaging difficult or impossible; (4) the extreme heat and contamination at the hot end of the line is damaging to any electronics used on inspection devices positioned at the hot end.
A solution to these problems is addressed in U.S. Pat. No. 5,437,702 issued Feb. 27, 1995 to Burns et al. for HOT BOTTLE INSPECTION APPARATUS AND METHOD, which is hereby specifically incorporated by reference for all that is disclosed therein. The Burns et al. patent discloses a non-contacting optical imaging inspection system that is located at the hot end of a bottle line. The optics and electronics employed are shielded from the harsh environment at the hot end of the production line by a fluid cooled housing. Clear panels in one of the housing walls enable the imaging devices within the housing to image passing bottles without the optics thereof being exposed to the harsh environment of the hot end. Fluid jets are provided adjacent to these clear panels in order to prevent contaminants from building up on the outer surface of the panels. Monitoring signals from the I.S. machine and the bottle conveyor are processed by data processing apparatus to determine the mold of origin of each bottle which is being imaged, thus obviating the need to read indicia on the surface of a glowing bottle. The image data from each bottle is analyzed to determine whether or not the bottle is defective.
Although this machine generally works well, it has been found that the clear panels of the fluid cooled housing still occasionally become dirtied, requiring maintenance and/or resulting in degradation of performance.
A solution to these problems associated with clear panels has been addressed in U.S. patent application Ser. No. 08/526,897 of Lucas for HOT BOTTLE INSPECTION APPARATUS AND METHOD, filed Sep. 12, 1995, which is hereby specifically incorporated by reference for all that is disclosed therein.
The Lucas application discloses fluid cooled housings in which the clear panels discussed above have been replaced with unobstructed openings which allow pressurized cooling fluid contained in the fluid cooled housing to escape therethrough. Although this arrangement effectively eliminates the problems associated with dirty panels discussed above, it has been found that the unobstructed openings generally allow cooling air to escape the housing at too great a rate, thus making it difficult to maintain positive pressure within the housing. It has further been found that eddy currents sometimes form around the edges of the unobstructed openings, causing contaminated air from the exterior of the housing to be drawn into the housing.